Hitherto, a considerable reduction in the total processing time of exposed black-and-white silver halide light-sensitive materials, and more particularly of those suited for use in medical diagnosis and in industrial non-destructive testing applications, has been achieved by persisting research leading to improvements on silver halide light-sensitive materials at one hand and processing agents, automatic processing machines and processing cycles on the other hand. In particular, reduction in processing time is very important for radiographic light-sensitive materials for medical use, because in an emergency every second counts for a medicine when a diagnosis should be made urgently in order to start a treatment.
In the case of industrial X-ray sensitive materials for non-destructive testing applications, it is necessary to coat a large amount of silver since the sensitivity of said materials to X-rays largely depends on the silver coverage thereof as direct-X-rays are captured, and consequently a much longer processing time is required for said industrial X-ray sensitive materials opposite to radiographic materials for medical use.
For medical radiographic imaging, rapid processing in an automatic processing machine is popular, and the total photographic processing time "dry-to-dry" ranges from 90 sec. to 3.5 min.
A substantially longer time from 5 min. to 11 min. is required for industrial X-ray sensitive materials. It is clear that under these circumstances, a further reduction in such a "dry-to-dry" processing time is desired.
In order to reduce the total photographic processing time, the processing time in each step, including development, fixing, washing (also called "rinsing") and drying should be shortened. A reduction in development time is generally known to be achieved by enhancing the activity of the developer. Increasing the concentration of the developing agent, pH of the developer solution, development temperature, addition of a developer activating agent (e.g. a hydrazine as in EP-A's 0 679 938 and 0 789 271) etc., in order to enhance the activity of the developer makes the cost of processing rise and/or makes preservation stability of the developer decrease. On the other hand, washing (rinsing) and drying times largely depend upon the thickness and the swelling degree of the coated layers that make part of a light-sensitive silver halide photographic material. Therefore, it is possible to reduce such processing times by previously using a hardener in a sufficient amount in order to increase the cross-linking degree of gelatin. However, the said increase causes a decrease in covering power which in turn requires an increase in silver coverage, in order to compensate for any decrease in sensitivity. Opposite thereto developability decreases and a further decrease in fixing speed is observed, thereby making the total processing cycle become more time-consuming.
In the patent literature EP-A 0 712 037, e.g., illustrates the combined use of an aminopolycarboxylic acid and a polyphosphonic acid sequestering agent in order to prevent aluminum sludging in hardening fixing baths when pH of the fixing solution is raised by an alkaline developer carried over from the developing solution. The fixing solution moreover shows a reduced sulfur dioxide emission because it is able to work at pH values higher than the well-known values within a classical standard pH range of from about 4.0 up to 4.5. Another composition as described in EP-A 0 726 491 makes use of .alpha.-ketocarboxylic acid compounds in order to reduce sulfur dioxide emission.
Processing in an automatic roller transport processor wherein processing is carried out without an intermediate washing step between the steps of developing and fixing, has been described, e g., in U.S. Pat. No. 3,545,971. In order to facilitate the use of a roller transport processor, both the developer and the fixer typically contain a hardening agent, with the hardening agent usually being an aldehyde in the developer and an aluminum salt in the fixer. Boric acid is often incorporated in the fixer used in the aforesaid process in order to prevent the formation of sludge resulting from precipitation of aluminum hydroxide when the fixer is contaminated by developer carry-over. Use of boric acid has been described, e.g., in U.S. Pat. No. 4,046,570. The hardening fixer composition described in this patent also contains a 1-hydroxy-alkylidene diphosphonic acid, in which the alkylidene group contains from 2 to 5 carbon a toms in order to retard formation of aluminum hydroxide. The 1-hydroxyalkylidene diphosphonic acid partially or completely replaces boric acid in the hardening fixer composition.
Another method to reduce the precipitation tendency of aluminum hydroxide has been described in Research Disclosure 17549. Therein a combination of a diphosphonic acid, such as a hydroxyalkylidene diphosphonic acid, and an aminopolycarboxylic acid, such as a 1,3-diamino-2-propanol tetraacetic acid, is used in order to process films in a roller transport processor wherein the processing is carried out without an intermediate washing step between the steps of developing and fixing. The tendency of aluminum hydroxide to precipitate in the hardening baths after carry-over of the aluminum salt hardening agent in a stabilizing bath is thereby clearly reduced. The diphosphonic acid and the aminopolycarboxylic acid are effective in the (color) stabilizing bath having a pH in the range from about 6 to about 11 in small concentrations such as amounts of each of about one gram per liter or less.
Japanese Patent Application 05/323 525 describes a black-and-white fixer solution comprising aminopolycarboxylic acids and/or phosphonic acids as chelating agent, preventing the water fur and odor. The fixer composition is substantially free from ammonium ions and substantially free from aluminum hardener, the amount of the hardener being lower than 0.1 mole/l, which is the minimum amount known in the art to give the fixer composition a hardening activity, as has been described e.g. in Research Disclosure 16768 and in U.S. Pat. No. 4,046,570.
In U.S. Pat. No. 5,300,405 a method of processing has been described using an optimized geometry in the dryer section of the processing in order to get suitable physical properties after drying of photographic films fixed in a fixer having a pH greater than 4.6 in running equilibrium conditions. Preferred developers are dihydroxy-benzene type developers, although other developers are not excluded. In that invention, a fixer has been described having a buffering capacity in the range between 0.5 to 0.8 mole/liter of a pH buffer agent, whereas usual fixers contain a pH buffer agent in a concentration of about 0.3 mole/liter.
From the side of the silver halide photographic material measures have been taken as disclosed in U.S. Pat. No. 5,230,993 wherein said material contains a polymer having a cationic site in a fixing solution, in order to improve fixing rate, dye stain and high-speed processing.
In order to further promote the objective of a very short total processing time it is advantageous to employ ammonium thiosulfate as a fixing agent, because it acts more rapidly than its alternatives such as sodium thiosulfate, as has been described in GB 1,290,026. Thus, a particularly desirable fixer is the one which contains ammonium thiosulfate and which is free from boric acid. However, it has been found that in those circumstances a very serious problem of crystal formation occurs. In particular, crystals are deposited from the fixer on the walls of the fixer tank and on the roller assemblies. In addition, the crystalline deposit displays a tendency to absorb additional fixer, thereby resulting in movement of "creep" along processor parts and tank walls. Research Disclosure 18728 discloses a number of agents incorporated in the hardening fixer solution which suppress crystal formation. Useful agents are, for example, aminopolyphosphonic acids, such as diethylenetriaminepenta-methylenephosphonic acid, and aminopolycarboxylic acids, such as 1,3-diamino-2-propanol tetraacetic acid.
EP-A 0 486 909 describes a fixing bath free from ammonium ions containing as a complexing agent, e.g., nitrilodiacetic monopropionic acid, useful in the processing of silver halide photographic materials. The bath exhibits good fixing speed and no deposition.
In praxis the fixer used in U.S. Pat. No. 5,300,405 has a pH value generally controlled at a pH of 4.6 or higher, preferably a pH from 4.6 to 6.0, and still more preferably from pH 4.7 to 5.5 as measured in running equilibrium conditions. Minimized odor thereby escapes from the fixer solution and provides minimized corrosion of the processing equipment and the surrounding environment. Since the fixer has a relatively weak hardening effect, increased drying loads are imposed on the photosensitive material being processed therewith. Even so, that invention makes use of a sophisticated drying process as defined above, accomplishing effective drying while eliminating locally uneven drying and drying marks.
The pH of common fixer solutions is normally in the range from 4.00-4.50, because at a higher pH value, especially more than 5.00, Al(OH).sub.3 becomes precipitated. On the other hand, a lower pH value is correlated with an undesired odor of environmentally unwanted sulfur dioxide due to decomposition of sulfites present in the fixer solution at the said lower pH values.
It should therefore be useful to have a photographic fixer composition showing a reduced tendency to form an aluminum hydroxide precipitate at pH values higher than those of standard fixer compositions as at the said higher pH value an advantageously reduced SO.sub.2 emission is highly desirable from an environmental point of view.